Measuring instruments for the continuous detection, dosage and adjustment of large quantities of flowable bulk materials that can be used to measure a given flowing mass flow, which take advantage of the Coriolis force, are known in the art. A measuring instrument of this kind will be designated below as a Coriolis measuring instrument and is known to the person skilled in the art, for example, also as a Coriolis flow-through scale or Coriolis scale. Coriolis measuring instruments essentially consist of a housing comprising an inlet tube, an outlet cone and a vane wheel that is able to rotate around a vertical axis of rotation. The vane wheel has a drive shaft that is preferably centrally routed through the top side of the housing and connected to a drive that is disposed outside of the housing.
The mass flow of a given bulk material that is to be detected is directed through the inlet tube toward the middle of the vane wheel, which rotates around the drive axis at a constant speed. The vane wheel has vanes that are disposed in a star-shaped manner around its axis of rotation and by which the inflowing bulk material is accelerated toward the outside. The Coriolis acceleration, upon which the movement of the mass particles is based, results in a momentum that acts on the vane wheel and that is proportionate to the mass flow of the bulk material flowing over the vane wheel. The Coriolis force acts counter to the torque that is provided by the drive of the measuring instrument and that is transferred via the drive shaft to the vanes; it can be detected by a torque measuring instrument that is disposed between drive and drive shaft.
EP 0 590 187 B1 discloses, for example, an embodiment of a mass flow measuring instrument that has the drive unit disposed above a rotating vane wheel. The drive shaft of the vane wheel is therefore aligned upward and routed through the top side of the housing of the apparatus. Consequently, the given bulk material must be fed from above through the inlet tube and at an angle around the drive shaft, then re-directed in a vertical direction shortly before entering the vane wheel. This angular feed of the bulk material has a disadvantageous effect on the accuracy of the measuring action of the device. Moreover, it is possible for foreign objects to get caught on the directional changeovers, which are necessary, thus blocking the bulk material feed.
An alternative embodiment of a Coriolis measuring instrument having an associated drive that is disposed below the vane wheel is known, for example, from DE 102 53 078 B3. The advantageous aspect of such embodiments operating according to the Coriolis principle is that the drive shaft does not have to be routed through the inflowing bulk material flow, which allows for directing the bulk material vertically from above and directly into the middle of the respective vane wheel, thus eliminating the need of having to redirect the flow immediately before the feed action. This vertical feed of the bulk material is advantageous for the accuracy of the measurement; and the bulk material is then discharged at a downward angle passing by the drive that is disposed in the center.
A similar embodiment with a drive shaft that is disposed below the vane wheel and with a central vertical bulk material feed is disclosed in DE 10 2004 060 045 B4; the drive herein is disposed laterally adjacent to the housing. The power transmission from the drive to the drive shaft and/or the vane wheel is achieved via a toothed belt or a spur gear pair located inside an encapsulated housing inside the bulk material chamber of the Coriolis measuring device. The bulk material is discharged centrally below the power transmission.
It is disadvantageous on these known embodiments that the drive is located at least in part inside the bulk material chamber thus impeding the bulk material discharge into the outlet cone of the measuring device. Furthermore, the affected drive components that are disposed inside the bulk material chamber are directly exposed to temperature stresses by the bulk material.
The known embodiments of Coriolis measuring instruments suffer considerably from a propensity of being subject to blockages, especially when the volume flows are small, due to the smaller inlet cross-sections and the smaller housing dimensions. But problems due to obstructions are also known from the conveyance of difficult bulk materials.